The invention concerns an osteosynthesis fixation system of a type among those used to treat degenerative or traumatic vertebral deformations, comprising anchoring screws for a vertebra, wherein at least one of the anchoring screws comprises a bone anchoring element provided at one of its ends with a screw head for coupling a connecting element to the bone anchoring element, wherein the bone anchoring element comprises a threaded rod in the vertebra, prolonged at the end by a coupling head for coupling with the screw head, the screw head comprising a body traversed longitudinally by a channel, wherein the channel has, in the lower portion, a receiving cavity for receiving the coupling head of the anchoring element.
The invention also concerns an anchoring screw intended for use with such a system.
The osteosynthesis system and the anchoring screw are intended particularly, but not exclusively, for treatment of major injuries to the vertebral column.
Use of spine stabilisation systems is known for the purpose of bone fusion in order to reduce a dorsolumbar fracture and stabilise the affected region. In the conventional method in itself, the spine stabilisation systems comprise bone anchoring elements designed to be fixed in the vertebrae involved in osteosynthesis (pedicle screws), connecting rods and means of coupling the connecting rods to these bone anchoring elements. Each bone anchoring element is coupled respectively to the connecting rod either by means of a connector, or directly. In the latter case, the bone anchoring element advantageously features a head arranged in order to receive the connecting rod. Conventionally, it is customary to resort to fixed-head anchoring elements in order to control reduction of the vertebrae.
Reduction of the fracture or straightening of the vertebrae is performed first of all by fixing the bone anchoring elements in the vertebrae involved in osteosynthesis and subsequently installing the connecting rod on the head of the bone anchoring element. The anchoring elements are fixed so as to extend appreciably perpendicularly in relation to the vertebra on which they are fixed, whilst the connecting rod must be positioned appreciably parallel to the vertebral column. A tightening nut is subsequently placed on each head, immobilising the connecting rod while allowing a rotational and translational movement of the latter on the head so as to allow performance of the reduction manipulations before final tightening of the nut and thus complete immobilisation of the connecting rod on the head. Straightening of the vertebra is performed gradually, by exerting traction, compression and/or expansion movements on each of the bone anchoring elements implanted on the vertebrae to be straightened with the aid of suitable instruments.
Mounting the connecting rod on the heads of bone anchoring elements often however proves troublesome.
Indeed, installing the connecting rods is the major disadvantage encountered with fixed-head anchoring elements. Depending on the position of the vertebrae, the heads of each bone anchoring element may display different inclinations and directions such that it proves difficult to place a connecting rod on all the heads of the bone anchoring elements. It is necessary in this case to adapt the connecting rods by means of appropriate curvatures. The more severe the deformation of the vertebral column, the more difficult installation of the connecting rods becomes. Moreover, the technique used does not systematically guarantee correct straightening of the vertebrae. Satisfactory straightening is all the more difficult when the curvature of the connecting rod is needed to be modified in order to allow installation of the rod on the heads of the bone anchoring elements.
In order to eliminate this disadvantage encountered with fixed-head anchoring elements, a number of surgeons resort to multiaxial-head anchoring elements. In a manner known per se, these elements comprise a head designed to receive a connecting rod, wherein the head is coupled to an end forming a ball-and-socket joint of a threaded rod. These bone anchoring elements offer the advantage of facilitating installation of the connecting rod on all the receiving heads, whereby the latter may be suitably oriented in order to receive the connecting rod. The disadvantage however of these multiaxial-head anchoring elements is that they cannot serve as a lever to straighten the vertebrae, as is the case with fixed-head anchoring elements, with the screw head of these elements not being completely immobilised on the threaded rod when the tightening nut is installed on the screw head in a tightening position allowing movement of the connecting rod. It is therefore necessary, once the bone anchoring elements, the connecting rod and the tightening nuts are in place, to proceed to reduce the vertebrae either by the method of positioning the patient or by techniques involving bending the connecting rod. These methods prove time-consuming and difficult however and do not ensure straightening of the threaded rod and hence of the vertebra in the axis of the screw head.
The invention aims to solve these problems by proposing an osteosynthesis system and an anchoring screw capable of being used with the osteosynthesis system allowing easier positioning of the connecting rods on the heads of the bone anchoring elements while retaining the functionality of the fixed-head anchoring elements (allowing straightening of the vertebrae).
The purpose of the invention is also to propose an osteosynthesis system and an anchoring screw allowing easier straightening and ensuring correct straightening.
The purpose of the invention is likewise to offer an anchoring screw of small dimensions.